FIG. 11, from U.S. Patent Pre-Grant Publication No. US 2015/0198227 A1 (Blough), illustrates prior art torque converter 320. Prior art torque converter 320 includes cover 321 arranged to receive torque, pump 322 non-rotatably connected to cover 321, turbine 323 including turbine shell 324, stator 325, turbine clutch 326, torsional vibration dampers 328 and 329, and torque converter clutch 330. Torque converter clutch 330 includes piston 337 arranged to be displaced in axial direction AD2 away from cover 321. Dampers 328 and 329 include output flanges 331 and 332, respectively, arranged to connect to an input shaft for a transmission. Torque converter 320 is a three-pass torque converter, with chambers 333, 334, and 335 controlling operation of clutches 326 and 330.
Torque converter 320 is designed to enable torque transmission through either clutch 326 or clutch 330. However, it is inefficient to simultaneously transmit torque through clutches 326 and 330, for example by simultaneously closing the clutches. To close clutch 326, chamber 334 is pressurized to displace turbine shell 324 in axial direction AD2. To minimize the amount of pressure needed to close clutch 326, pressure in chamber 333 is kept low. However, pressurizing chamber 334 urges piston 337 in direction AD1, which opens clutch 326. To close clutch 330, chamber 335 is pressurized to displace piston 337 in direction AD2. To simultaneously close clutches 326 and 330, chambers 334 and 335 must both be pressurized. Thus, chamber 334 is pressurized to obtain the desired clamping of clutch 326 and chamber 335 must be pressurized to obtain the desired clamping of clutch 330 plus counteract the pressure in chamber 334. This leads to an undesirable increase in the energy output of the pump supplying fluid pressure to torque converter 320. Further, the fluid pressure available to a torque converter is typically supplied by a pump in a transmission and is limited due to operating requirements for the transmission. Therefore, there may not be sufficient fluid pressure available to properly pressurize both chambers 334 and 335. In addition, when clutch 326 is closed, there are energy losses due to the cooling flow from chamber 334 to chamber 333 through cooling channels typically found in clutch friction material. Specifically, pressure in chamber 333 is kept deliberately low to reduce pressure needed in chamber 334, but the pressure differential between chambers 333 and 334 undesirably increases flow out of chamber 334, which must be replenished by the pump.